Replication of human retroviruses, such as, for example, human immunodeficiency virus type I (HIV-1), entails an ordered pattern of viral gene expression. This regulated gene expression is dependent upon the sequence-specific interactions of two viral regulatory proteins, Tat and Rev, with their respective sites on viral RNA. Tat is a transcriptional activator, whereas Rev acts posttranscriptionally to increase the cytoplasmic accumulation of the viral gag-pol and env messenger RNAs (mRNAs).
Because Tat and Rev are critical for viral replication they are attractive targets for therapeutic intervention. To date, three strategies have been attempted to reduce the levels of these viral regulatory proteins or to block their action. First, antisense nucleic acids directed against Rev mRNA have been used to decrease the steady-state level of Rev protein. A second strategy is to sequester (titrate) the regulatory protein by the introduction of a large excess of small "decoy" RNA that contains a high affinity protein-binding site. For example, retroviral vectors expressing the Tat-binding site TAR can inhibit viral replication in cultured cells. A third approach is to express dominant negative mutants of the viral regulatory proteins. For example, Rev derivatives bearing mutations within a discrete C-terminal region abolish Rev activity, and these mutants can inhibit wild-type Rev in a cotransfection assay.
A major difficulty inherent in these three strategies is the problem of delivering the therapeutic agent, which is either a nucleic acid or a protein, to target cells within the body. Thus, there is a need in the art for methods and compositions that provide easily deliverable biologically active agents capable of inhibiting the interaction of Rev and/or Tat proteins.
One class of biologically active small organic molecules is the bisamidines, which were known to interact with the minor groove in DNA. Examples of bisamidine compounds include pentamidine and its analogues, which were first developed as antiprotozoal agents (Harding, R. D., Trans. R. Soc. Trop. Med. Hyg., 39:99-124, 1945; Napier et al., Indian Med. Gaz., 78:177-183, 1943) and now are used for the treatment of Pneumocystis carinii infections (Greenidge et al., Mol. Pharmacol. 43:982, 1993; Tidwell et al., U.S. patent application Ser. No. 4,933,347), and related aromatic amidines useful in inhibiting cell fusion induced by respiratory syncytial virus (Tidwell et al., U.S. patent application Ser. No. 4,619,942). Other 2,5-bis(4-amidinophenyl)furans have been tested for antiprotozoal, particularly antitrypanosomal, activity (Boykin et al., J. Med. Chem. 20:531, 1977; Dann et al., Liebigs Ann. Chem., 160, 1975).